This invention relates generally to heat pipes, and more specifically to methods for making sintered metal heat pipe wicks with arteries.
Heat pipes use successive evaporation and condensation of a working fluid to transport thermal energy, or heat, from a heat source to a heat sink. Because most fluids have a high heat of vaporization, heat pipes can transport in a vaporized working fluid very large amounts of heat. Further, the heat can be transported over very small temperature differences between the heat source and heat sink. Heat pipes generally use capillary forces through a porous wick to return condensed working fluid, or condensate, from a heat pipe condenser section (where transported thermal energy is given up at the heat sink) to an evaporator section (where the thermal energy to be transported is absorbed from the heat source).
Heat pipe wicks are made by a variety of different methods. The most common method is by wrapping metal screening or felt metal around a cylindrically shaped mandrel, inserting the mandrel and wick inside a heat pipe container and then removing the mandrel. Another method produces a heat pipe wick of sintered metal. Sintered metal wicks are generally made by filling powered metal into the space between a mandrel and the inside surface of a heat pipe container and then heating the powder to sinter together the individual particles and make a porous wick. The mandrel, having been previously surface treated to aid separation, is then removed from inside the sintered wick. Sintered metal heat pipe wicks may also be made, as taught in companion application Ser. No. 07/261,809, by coating the inside of a spinning heat pipe container with a slurry of metal powder mixed into a viscous binder drying the spinning wick to form a green wick, then stopping the container and wick and heat treating the wick to disintegrate the binder and leave a sintered metal wick. This new method of making sintered metal heat pipe wicks, referred to hereinafter as the spinning pipe method, produces higher performance wick than has been known before in the art.
Prior art heat pipe wicks, whether wrapped, sintered or made by other methods, are generally greatly improved by the addition of longitudinal channels or arteries. The channels or arteries may be either entirely within the wicks or on the inside surface of the heat pipe container in contact with the wick material. While the small pore size of most wick material provides high capillary pumping forces, the resulting convoluted passages for the flow of liquid cause a viscous drag which reduces the total fluid flow. The addition of relatively straight open channels or arteries provides a low loss path for the flow of large amounts of liquid working fluid pumped by the small pores of the porous wick material.
The prior art teaches a variety of methods for producing such channels or arteries. One method is to build the wick around a series of rods or tubes and then pull out the rods or tubes to leave arteries through the wick. Alternately, appropriate etchants have been used to dissolve the rods or tubes and leave arteries through the wick.
While these methods for making arteries through wicks may possibly be adapted for use with the spinning pipe method, adapting them will be awkward and cumbersome. Also, when using these methods, it is often difficult to accurately position the arteries and arteries are not perfectly formed or sized.
Thus it is seen that there is a need for a method for making arteries through wicks made by the spinning pipe method that is neither unwieldy nor complicatedm, but simple and direct, and which produces accurately positioned, sized and shaped arteries.
It is, therefore a principal object of the present invention to provide a method for making arteries in heat pipe wicks made by the spinning pipe method that is uncomplicated and straightforward, and which produces extraordinarily accurately sized, shaped and positioned arteries.
It is an advantage of the invention that it easily makes arteries of varied sizes and shapes.